/*--------------------------------------------------------------------*/ 
/*  Problem chapter7_7                                                */ 
/*                                                                    */ 
/*  This program computes the average power of a specified columns    */   
/*--------------------------------------------------------------------*/ 
 
#include <iostream> 
#include <string> 
#include <fstream> 
using namespace std; 
 
const int NCOLS = 7; 
const int NROWS = 10; 

double col_ave (double x[][NCOLS], int col);
 
int main( ) 
{ 
   /*  Define variables.  */ 
   double ave, power[NROWS][NCOLS]; 
   int col; 
   string filename;
   ifstream fin; 
 
   /*  Open input file.  */ 
   cout << "Enter the name of the input file: "<<endl; 
   cin >> filename; 
   fin.open(filename.c_str() ); 

   if(fin.fail()) 
   { 
      cerr << "error opening file " << filename << endl; 
      return 0; 
   }
 
   /*  Read data.  */ 
   for (int i=0; i<NROWS; i++) 
      for (int j=0; j<NCOLS; j++) 
      { 
         fin >> power[i][j];  
      } 
 
   /* reference the function to compute the column average.  */ 
   cout << "Which column do you want the average? " <<endl; 
   cin >> col;

   ave = col_ave(power, col);

   cout << "The column " << col << " has average value: " << ave << endl; 
 
   return 0; 
}


/* This function computes the average of the col column */ 

double col_ave(double x[][NCOLS], int col)
{ double sum = 0.0, ave;
  for (int i=0; i < NROWS; i++)
     {
       sum = sum + x[i][col]; 
     }
  ave = sum / NROWS;
  return ave;
}